1. Field of the Invention
The present invention relates to a method for producing an electron source having electron emitting portions. The present invention also relates to an electron source produced by the producing method thereof, an image forming apparatus using the electron source, and an apparatus for producing the electron source.
2. Related Background Art
The electron emitting elements conventionally known are roughly classified under two types using thermionic emission elements and cold emission elements. Examples of the cold emission elements are electron emitting elements of a field emission type (hereinafter referred to as "FE type"), a metal/insulator/metal type (hereinafter referred to as "MIM type"), a surface conduction type, and so on. Examples of the FE type known are those disclosed in W. P. Dyke & W. W. Doran, "Field Emission," Advance in Electron Physics, 8, 89 (1956), C. A. Spindt, "Physical Properties of thin-film field emission cathodes with molybdenum cones," J. Appl. Phys., 47, 5248 (1976), and so on. An example of the MIM type known is the one as disclosed in C. A. Mead, "Operation of Tunnel-Emission Devices," J. Appl. Phys., 32, 646 (1961), for example.
An example of the surface conduction type electron emitting element is the one as disclosed in M. I. Elinson, Radio Eng. Electron Phys., 10, 1290 (1965), for example.
The surface conduction type electron emitting element emits electrons when a current is allowed to flow in parallel to the film plane through a thin film of a small area formed on a substrate. There are reports on this surface conduction type electron emitting element; for example, those using Au thin film [G. Dittmer: Thin Solid Films, 9, 317 (1972)], using In.sub.2 O.sub.3 /SnO.sub.2 thin film [M. Hartwell and C. G. Fonstad: IEEE Trans. ED Conf., 519 (1975)], using carbon thin film [Hisashi Araki et al.: Vacuum, Vol 26, No. 1, p 22 (1983)], and so on.
FIG. 21 schematically shows the element configuration of M. Hartwell, as described above, as a typical example of these surface conduction type electron emitting elements. In the same figure reference numeral 1 designates a substrate. Numeral 4 represents a conductive thin film, which is, for example, a thin film of metal oxide formed in a pattern of H-shape by sputtering. An electron emitting section 5 is formed by an electrification process called "electric forming" as detailed hereinafter. The distance L1 between the element electrodes in the drawing is set to 0.5 to 1 mm and the width W' to 0.1 mm. Since the position and shape of the electron emitting section 5 are not described specifically, the element is illustrated as a schematic view.
In these conventional surface conduction type electron emitting elements, the electron emitting section 5 is formed generally by preliminarily subjecting the conductive thin film 4 to the electrification process called the electric forming prior to emission of electron. The electric forming is formation of the electron emitting section by electrification, which is achieved, for example, by applying a dc voltage or very slowly increasing voltages to the both ends of the conductive thin film 4 to effect electrification, so as to locally break, deform, or alter the conductive thin film, thereby forming the electron emitting section 5 kept in an electrically high resistance state. The electron emitting section 5 has a crack produced in a part of the conductive thin film 4 and emits electrons from near the crack. The surface conduction type electron emitting element processed by the aforementioned electric forming process emits electrons from the above-stated electron emitting section 5 when the voltage is applied to the conductive thin film 4 to allow the current to flow through the element.
The surface conduction type electron emitting elements described above have the advantage that a lot of surface conduction type emitting elements can be arrayed over a large area, because the structure is simple and they can be produced using the conventional semiconductor fabrication technology. There are researches on such various applications as to make use of this feature. Examples of the applications are image forming apparatus such as charged electron beam sources and display devices.
FIG. 20 shows the structure of the electron emitting element disclosed in the official gazette of Japanese Laid-open Patent Application No. 2-56822 filed by Applicant. In the same figure, numeral 1 denotes a substrate, 2 and 3 element electrodes, 4 a conductive thin film, and 5 an electron emitting section. There are a variety of methods for producing this electron emitting element. For example, the element electrodes 2 and 3 are formed on the substrate 1 by the vacuum thin film technology and photolithography etching technology in the ordinary semiconductor processes.
Then the conductive thin film 4 is formed by a dispersion coating method such as spin coating, or the like. After that, the voltage is applied to the element electrodes 2, 3 to carry out the electrification process, thereby forming the electron emitting section 5.
This production method in the conventional example has drawbacks that large-scale photolithography etching facilities are necessary and indispensable for forming the elements over a large area, the number of steps is also large, and the production cost is thus high. In view of these drawbacks, there are proposals on a method for directly dispensing droplets of a solution containing a metal element by the ink jet method, as a method for patterning the conductive thin film of the surface conduction type electron emitting elements without use of the semiconductor processes (for example, as disclosed in Japanese Laid-open Patent Application No. 8-171850).
Since the conventional ink jet method as described in the official gazette of Japanese Laid-open Patent Application No. 8-171850 etc. is a method for directly dispensing a droplet from a droplet dispensing device 6 having a single nozzle as shown in FIGS. 19A, 19B, and 19C and since a lot of time is needed for scribing of one substrate in case an area of substrate is increased more and more, there is the limit of increase in throughput, however.
The present invention provides a method for producing an electron source by adopting a novel method for dispensing the material for the electron emitting section.